Configuration file work
Got configuration options set up a little bit nicer.
Fixes #1 -- Updated autoconf/automake stuff

`make distcheck` seems to be working okay, for now.

The configuration file (via config.h.in) looks pretty clean and tidy,
I think it's suitable for use in the library now.
Fixes #1 - Corrected mingw issue in string.cc (check __MINGW__)

This fix is pretty self-explanatory. I've included stdlib.h to ensure that
__MINGW__ is defined, and check if this is defined in addition to testing if
we're building on MSVC.

This will probably still be broken on Cygwin, but everyone hates Cygwin so it
might not be much of an issue. Still, simply testing if we're building on
Windows is probably good enough.
Merge pull request #1 from caitp/issue-1

Update autoconf/automake files to produce (namespaced) config.h, fix make distcheck